JP3907794B2 - Autofocus device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an autofocus device that automatically adjusts the focus of a subject in various imaging devices such as a surveillance camera and a video camera. In particular, the present invention is a so-called automatic focus adjustment based on a subject image obtained through an optical system. The present invention relates to a passive autofocus device.
[0002]
[Prior art]
  As a passive autofocus device as described above, for example, an optical system extracts a high-frequency component from a video signal obtained from an image sensor, and maximizes the level (size) of the extracted high-frequency component. What drives is known. This utilizes the fact that the level of the high-frequency component correlates with the sharpness of the subject image formed by the optical system, that is, the position where the level of the high-frequency component is maximum is the sum of the optical system. It becomes a focal position.
[0003]
  Here, when a general subject is photographed (for example, when a special subject such as a uniform wall surface is photographed over the entire field of view of the camera), the position of the optical system (for example, the amount of extension of the focus lens) and this optical An example of the relationship between the level of the high frequency component and the position of the system is shown in FIG. In this case, the level of the high-frequency component changes approximately in a mountain shape with respect to the position of the optical system, as indicated by a solid line graph in FIG. And the position corresponding to the top P of this mountain-shaped graph becomes an in-focus position. Therefore, in order to focus on the subject, it is only necessary to find the top P of the graph and move the optical system there. In order to realize this, the top P is found by a conventionally well-known hill climbing method.
[0004]
  That is, in the same figure, if the optical system is at point O, for example, first, the optical system is first moved by a predetermined amount N (to point Q) in a predetermined direction, for example, the FAR (far distance) direction. The level change of the high frequency component at this time is monitored. When this level change tends to increase, it is assumed that the optical system is moving toward the top P, that is, in the in-focus direction, and the optical system is further moved in the same direction. On the other hand, when the level change tends to decrease as shown in the figure, it is considered that the optical system is moving in a direction opposite to the top P, that is, in a so-called defocus direction. Therefore, in this case, the optical system is moved in the NEAR (proximity) direction opposite to the above direction.
[0005]
  Then, the level of the high-frequency component is monitored while moving the optical system toward the top P as described above until the level of the high-frequency component changes from an increasing tendency to a decreasing tendency and decreases by a predetermined level α (point R). Until the position of the top P is confirmed. Then, after confirming the position of the top P in this way, a series of focusing operations can be realized by returning the optical system to the position of the top P obtained by the confirmation.
[0006]
  By the way, according to this conventional hill-climbing method, the optical system is moved at a relatively slow speed in order to find the top P accurately. Therefore, there is a problem that a relatively long time is required for the focusing operation.
[0007]
  Further, it is known that the absolute value of the level of the high-frequency component generally changes according to the illuminance (brightness) of the subject. For example, when the illuminance of the subject is low, the level of the high-frequency component is smaller than the solid line graph as shown by the dotted line graph in FIG. On the other hand, according to the conventional hill-climbing method, the amount of reduction α from the top P to the R point is always constant regardless of the illuminance of the subject. Therefore, when the illuminance of the subject is reduced as described above, the distance from the top P to the R point is increased, and the amount of movement of the optical system is increased correspondingly, and the focusing operation takes more time. is there.
[0008]
  Furthermore, depending on the performance and quality of the optical system, for example, as shown in FIG. 8, relatively small peaks P ′ and P ′ may occur at a so-called defocused position other than the top (focus position) P. These peaks P ′ and P ′ are generally called pseudo resolution (or spurious resolution), and if an optical system is provided at the apex of these pseudo resolutions P ′ and P ′. When moved, it is known that undesired phenomena such as two-line blurring and black-and-white reversal occur in the subject image. However, when such false resolutions P ′ and P ′ occur, in the focusing operation by the conventional hill climbing method, the false resolutions P ′ and P ′ and the focus position P are erroneously recognized. Sometimes. For example, it is assumed that the first position (O point) of the optical system is in a valley between the in-focus position P and the false resolution P ′ on the FAR side (left side in the figure), as shown in the figure. In this case, when the optical system is first moved to the FAR side by a predetermined amount N, the FAR side false resolution P ′ is erroneously recognized as the in-focus position P.
[0009]
[Problems to be solved by the invention]
  That is, the problems to be solved by the present invention are that the focusing operation by the conventional hill climbing method takes time to find the focusing position P, and the false resolutions P ′ and P ′ are combined. It is misrecognized as a focal position.
[0010]
  Accordingly, an object of the present invention is to provide an autofocus device that can find the in-focus position P in a shorter time than the conventional hill-climbing method. Further, it is an object of the present invention to find the correct in-focus position P without being affected by these false resolutions P ′ and P ′.
[0011]
[Means for Solving the Problems]
  In order to achieve the above-described object, the first invention provides an optical system having an imaging function, an imaging means for converting a subject image formed by the optical system into a video signal, and the video signal. Extraction means for extracting high-frequency components from,Extracted high frequency componentsAnd a control means for generating a control signal based on the detected level, and an image formed by the optical system and the imaging means by moving the optical system along the optical axis direction based on the control signal. Driving means for changing the distance between the surfaces,To do. AndThe control means moves the optical system in the predetermined direction at a high speed when the optical system moves in the predetermined direction, and when the level of the high-frequency component tends to increase in the initial operation. The high-speed operation moves the optical system at a high speed in a direction opposite to the predetermined direction when the level of the high-frequency component is decreasing, and the high-frequency component level changes from an increasing trend to a decreasing trend in this high-speed operation. A low-speed operation that moves the optical system in a direction opposite to the moving direction of the optical system in the high-speed operation at a speed slower than the moving speed in the high-speed operation And after confirming that the level of the high-frequency component changed again from an increasing trend to a decreasing trend in this low-speed operation,At the position recognized as the in-focus position of the optical system with respect to the imaging surface of the image sensorThe control signal is generated so as to cause the driving means to perform a fine adjustment operation for moving the optical system.
[0012]
  Further, the control means compares the maximum value of the high-frequency component level in the low-speed operation with the second level, and when the maximum value is equal to or higher than the second level, the position of the optical system corresponding to the maximum value. Are recognized as in-focus positions. On the other hand, when the maximum value is smaller than the second level, the control signal is generated so as to move the optical system over the entire range in which the optical system can move, and the movement period of the optical system over the entire range. The position where the level of the high-frequency component is maximum is recognized as the in-focus position. The second level is larger than the peak value of the false resolution when the false resolution occurs in the high frequency component and smaller than the level of the high frequency component when the optical system is at the in-focus position. An autofocus device with a value set.
[0013]
  In this case, when the optical system is moved, the level of the high-frequency component changes in a roughly mountain shape as shown in FIG. 7 described above with respect to the movement position of the optical system, for example. It is assumed that P is the in-focus position.
[0014]
  That is,This first inventionAccordingly, the optical system moves in a predetermined direction in the initial operation. In this initial operation, when the level of the high-frequency component tends to increase, it can be considered that the optical system is moving toward the in-focus position. And move at higher speed in the same direction. On the other hand, in the initial operation, when the level of the high frequency component tends to decrease, it can be considered that the optical system is moving in the direction opposite to the in-focus position, that is, in the defocus direction. Therefore, in this case, the optical system moves at a high speed in a direction opposite to the initial operation in the high speed operation.
[0015]
  Then, in the high-speed operation, the optical system moves from the increasing tendency to the decreasing tendency until the optical system moves from the time when the high-frequency component level decreases to a certain first level amount, and then enters the low-speed operation. In this low-speed operation, the optical system moves at a low speed in the direction opposite to the moving direction in the high-speed operation, and confirms the position at which the level of the high-frequency component changes again from the increasing tendency to the decreasing tendency, that is, the in-focus position. To do. Then, after confirming the in-focus position, the optical system moves to the in-focus position confirmed by the low-speed operation in the fine adjustment operation, for example, at high speed, and ends the series of in-focus operations.
[0016]
  That meansThis first inventionAs with the prior art described above, the in-focus position is obtained by a hill-climbing method.This first inventionAccording to the above, in the series of focusing operations, the optical system operates at a low speed during the low speed operation (specifically, the level of the high frequency component is reduced by the first level amount from the level at the in-focus position). Until the confirmation of the in-focus position. Further, since the in-focus position is confirmed during this low speed operation, accurate focus adjustment can be realized.
[0017]
  However, when the false resolutions P ′ and P ′ as shown in FIG. 8 occur, the peaks of the false resolutions P ′ and P ′ may be erroneously recognized as in-focus positions.
[0018]
  Therefore, in the first invention, the control means further compares the maximum value of the level of the high frequency component in the low speed operation with a certain second level. Here, for example, the maximum value is the second value. When the level is equal to or higher than the level, the control unit recognizes the position of the optical system corresponding to the maximum value as the in-focus position. Then, as described above, in the fine adjustment operation, the optical system is moved to the position recognized as the focus position. On the other hand, when the maximum value of the high-frequency component level in the low-speed operation is smaller than the second level, the maximum value is recognized as the peak of false resolutions P ′ and P ′. Then, the optical system is moved, for example, at a low speed over the entire range in which the optical system can move, and the position where the level of the high-frequency component is maximum during this movement period is recognized as the in-focus position. Finally, in the fine adjustment operation, the optical system is moved to the position recognized as the focus position, and the series of focus operations is completed.
[0019]
  As described above, as the second level, a value that is larger than the peak values of the false resolutions P ′ and P ′ and smaller than the level (maximum value) of the high-frequency component at the in-focus position is set. The
[0020]
  In this first invention,First level varying means for receiving the video signal and changing the first level amount according to the signal level of the input video signal, that is, the illuminance (or brightness, contrast) of the subject., May be provided.
[0021]
  That is, as described above, the level change of the high-frequency component becomes steeper near the in-focus position as the illuminance of the subject is higher (brighter), and the level change becomes slower as the illuminance of the subject is lower (darker). . Therefore, for example, if the first level amount is constant regardless of the illuminance of the subject, the in-focus position and the position where the level of the high frequency component is reduced from the maximum value by the first level amount (the optical system has a high speed). The distance between the movement position and the low-speed movement becomes longer as the illuminance of the subject decreases. That is, the lower the illuminance of the subject, the greater the amount of movement of the optical system, and the longer the focusing operation.
[0022]
  On the contrary,If the first level variable means as described above is provided, the lower the illuminance of the subject, the smaller the first level amount is set, and the higher the illuminance of the subject, the larger the first level amount is set. .Accordingly, even when the illuminance of the subject is low, the moving distance of the optical system (that is, the in-focus position and the level of the high-frequency component is the maximum value from the maximum value as compared with the case where the first level is constant (invariable). The distance between the position that decreases by the level of 1 and the distance) does not increase. That is, when the illuminance of the subject is low, the first level is unchanged (constant).CaseAs a result, the time required for the focusing operation can be shortened.
[0023]
  Furthermore, in the first invention,Second level variable means for inputting the video signal and changing the second level according to the signal level of the input video signal;, May be provided.
[0024]
  That is,It is also known that, in general, the peak values of the false resolutions P ′ and P ′ change according to the illuminance of the subject, in the same manner as the level of the high-frequency component changes according to the illuminance of the subject.In particular,When the illuminance of the subject is high (bright), the peak values of the pseudo resolutions P ′ and P ′ are high, and when the illuminance of the subject is low (dark), the peak values of the pseudo resolutions P ′ and P ′ are low.
[0025]
  Here, for example, it is assumed that the second level is constant regardless of the illuminance of the subject and is a relatively low level. In this case, when the illuminance of the subject increases, the peak values of the false resolutions P ′ and P ′ may exceed the second level. As described above, when the peak values of the false resolutions P ′ and P ′ exceed the second level,Low speed operation (and high speed operation)In this case, there is a problem that it is impossible to determine whether the position where the level of the high-frequency component is maximum is the true in-focus position P or the peaks of the false resolutions P ′ and P ′.
[0026]
  In contrast to the above, it is assumed that the second level is relatively high and constant regardless of the illuminance of the subject. In this case, when the illuminance of the subject becomes extremely low, the maximum value of the high-frequency component level, that is, the high-frequency component level at the in-focus position P may be lower than the second level. So, for example, onLowEven if the in-focus position P is found in the high speed operation, it may be erroneously recognized as the peak of the false resolutions P ′ and P ′. In the case of such erroneous recognition, the optical system moves at a low speed in the entire movement range from the FAR side end to the NEAR side end as described above, and therefore it takes a long time for the focusing operation. Will be applied.
[0027]
  On the contrary,If the second level variable means as described above is provided,The second level changes according to the illuminance of the subject, that is, according to the false resolutions P ′ and P ′ and the peak value of the entire high-frequency component (specifically, when the illuminance of the subject is high, the second level is changed). Is set high and the second level is set low when the illuminance of the subject is low). Therefore,Low speed operationIt is possible to correctly determine whether the position where the level of the high-frequency component is maximum is the true in-focus position P or the peak of the false resolutions P ′ and P ′ regardless of the illuminance of the subject.
[0028]
  According to a second aspect of the present invention, there is provided an optical system having an imaging function, imaging means for converting a subject image formed by the optical system into a video signal, and extraction means for extracting a high frequency component from the video signal. Control means for detecting the level of the extracted high-frequency component and generating a control signal based on the detection level; and moving the optical system along the direction of the optical axis based on the control signal; Driving means for changing the distance between the imaging means and the imaging plane of the imaging means. Then, the control means moves the optical system in a predetermined direction when the initial operation of moving the optical system in a predetermined direction and the level of the high-frequency component changes or increases in the initial operation. When the optical system moves to one end of the movable range without changing the level of the high frequency component more than the third level difference in the initial operation, or the level of the high frequency component tends to decrease. A high-speed operation that moves the system at a high speed in the direction opposite to the predetermined direction, and the high-frequency component level in this high-speed operation has changed from an increasing trend to a decreasing trend, and when the level has decreased by a first level amount. In this low speed operation, the optical system is moved in a direction opposite to the moving direction of the optical system in the high speed operation at a speed slower than the movement speed in the high speed operation. And the fine adjustment operation for moving the optical system to the position corresponding to the maximum value of the high frequency component level in the low speed operation after confirming that the level of the high frequency component has changed again from the increasing tendency to the decreasing tendency. The control signal is generated so as to be executed by the means. Then, the third level difference is larger than the peak-to-peak value of the false resolution when the false resolution occurs in the high-frequency component and smaller than the peak-to-peak value of the entire high-frequency component. This is an autofocus device with a value (level difference) set.
[0029]
  That is, also in the second invention, as in the first invention, the optical system moves in a predetermined direction in the initial operation. In this initial operation, when the level of the high frequency component tends to increase, the optical system moves at a higher speed in the same direction as the initial operation in the high speed operation. On the other hand, when the level of the high frequency component tends to decrease in the initial operation, the optical system moves at a high speed in the direction opposite to the initial operation in the high speed operation. Then, in the high-speed operation, the optical system moves from the increasing tendency to the decreasing tendency and moves from the time when the high-frequency component level decreases to a certain first level amount, and then enters the low-speed operation. In this low-speed operation, the optical system moves at a low speed in the direction opposite to the moving direction in the high-speed operation, and confirms the position at which the level of the high-frequency component changes again from the increasing tendency to the decreasing tendency, that is, the in-focus position. To do. Then, in the fine adjustment operation, the optical system moves, for example, at a high speed to the in-focus position obtained by checking with the low speed operation, and ends the series of focus operations.
[0030]
  here,Now, it is assumed that the false resolutions P ′ and P ′ are generated, and the optical system is positioned on the false resolutions P ′ and P ′. When the focusing operation is started in this state, the optical system moves on the false resolutions P ′ and P ′ in the initial operation. in this case,For example, simplyThe moving direction of the optical system in the high-speed operation is determined based on the increasing / decreasing tendency of the level of the high-frequency component by moving on the false resolutions P ′ and P ′.Then,As a result, an incorrect moving direction is determined.
[0031]
  Therefore, in the second invention,In the initial operation, the level of the high frequency component isIt is larger than the peak-to-peak value of the false resolutions P ′ and P ′ and smaller than the peak-to-peak value in the entire high-frequency component.Only when the third level difference or more changes, the moving direction of the optical system in high-speed operation is determined based on the increasing / decreasing tendency of the level change. In the initial operation, when the optical system moves to one end of the movable range (for example, the FAR side end or the NEAR side end) before the level of the high frequency component changes by the third level difference or more. The optical system can be regarded as moving on the false resolutions P ′ and P ′. Therefore, in this case, the direction opposite to the moving direction in the initial operation is set as the moving direction of the optical system in the high-speed operation.
[0032]
  In the second invention as well, similarly to the first invention, first level variable means for changing the first level amount in accordance with the signal level of the video signal may be provided.
[0033]
  Also,Third level variable means for inputting the video signal and changing the third level difference according to the signal level of the input video signal., May be provided.
[0034]
  That is, it is assumed that the third level difference is constant regardless of the illuminance of the subject. in this case,When the illuminance of the subject increases, the peak-to-peak values of the false resolutions P ′ and P ′ may be larger than the third level difference. As described above, when the peak-to-peak value of the false resolutions P ′ and P ′ becomes larger than the third level difference, the optical system moves on the false resolutions P ′ and P ′ in the initial operation. This causes a problem that it is impossible to determine whether or not it is.On the other hand, when the illuminance of the subject becomes extremely low, the peak-to-peak value of the entire high-frequency component may be smaller than the third level difference. In this case, since the level of the high frequency component does not change more than the third level difference in the initial operation, the direction opposite to the moving direction in the initial operation is always the moving direction of the optical system in the high speed operation. Is done. That is, the wrong moving direction may be determined.
[0035]
  On the contrary,If the third level variable means as described above is provided,When the illuminance of the subject is high, the third level difference is set large, and when the illuminance of the subject is low, the third level difference is set small. Therefore, the moving direction of the optical system in high-speed operation can be obtained accurately.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
  An embodiment of an autofocus device according to the present invention will be described with reference to FIGS. Note that the autofocus device of the present embodiment also extracts a high-frequency component from the video signal obtained by imaging the subject, and extracts the extracted high-frequency component, similarly to the above-described conventional passive autofocus device. Basically, the position where the level of the maximum is found by the hill-climbing method.
[0037]
  FIG. 2 is a block diagram showing a schematic configuration of the present embodiment. In FIG. 1, reference numeral 1 denotes an optical system having an imaging (condensing) function such as a focus lens. A subject image of a subject (not shown) projected by the optical system 1 is received by, for example, a CCD image sensor 2. An image is formed on the surface 2a and converted into a video signal here. The video signal converted by the image sensor 2 is amplified by the preamplifier 3 and then subjected to various signal processing by a video signal processing circuit (not shown).
[0038]
  The video signal amplified by the preamplifier 3 is also input to an illuminance detection circuit 4 and a high pass filter (hereinafter referred to as HPF) 5. Of these, the illuminance detection circuit 4 indirectly detects the illuminance of the subject from the amplitude of the video signal, and the detection result is sent to, for example, a control circuit 6 having a CPU (Central Processing Unit) (not shown). input. On the other hand, the HPF 5 extracts a high frequency component from the video signal, and the high frequency component extracted by the HPF 5 is also input to the control circuit 6.
[0039]
  The control circuit 6 generates a control signal based on the input illuminance information and high frequency component of the subject, and supplies this control signal to the drive circuit 7. The drive circuit 7 drives a focus drive motor (hereinafter simply referred to as a motor) 8 in accordance with the supplied control signal, thereby adjusting the distance between the optical system 1 and the light receiving surface 2a of the image sensor 2. To do.
[0040]
  The control circuit 6 generates the control signal based on a component in a so-called ranging area that is set in advance as a focus adjustment area among the illuminance information and the high-frequency component input thereto. . The motor 8 has a stepping motor configuration, for example. Although not shown, the end detection means for detecting that the optical system 1 has reached the end of the moving range of the optical system 1, that is, the NEAR side end and the FAR side end, respectively. The output signal of this end detection means is also input to the control circuit 6. The end detection means is constituted by a light emitting / receiving element such as a photo interrupter.
[0041]
  By the way, when a general subject is photographed with the configuration shown in FIG. 2 (for example, when a special subject such as a uniform wall surface is photographed over the entire field of view of the camera), the position of the optical system 1 (that is, the optical system 1 and The relationship between the distance from the light receiving surface 2a of the image pickup device 2) and the level of the high-frequency component with respect to the position of the optical system 1 is, for example, as shown in FIG. That is, the level of the high-frequency component changes approximately in a mountain shape with respect to the position of the optical system 1 as shown by a solid line graph in the figure, and the position corresponding to the top P of this mountain-shaped graph is It becomes a focal position.
[0042]
  Therefore, in the present embodiment, assuming that the optical system 1 is at a point O, for example, first, the optical system 1 is first moved in a predetermined direction, for example, the FAR direction by a certain distance, for example, N pulses (Q point). And moving at a relatively slow speed, and monitoring the level change of the high frequency component at this time. When this level change tends to increase, it is considered that the optical system 1 is moving toward the in-focus position P, and the optical system 1 is further directed in the same direction. Move at speed. On the other hand, when the level change tends to decrease as shown in the figure, it is considered that the optical system 1 is moving in a direction opposite to the in-focus position P, that is, in a so-called defocus direction. . Therefore, in this case, the optical system 1 is moved at a relatively high speed in the NEAR (proximity) direction opposite to the above direction.
[0043]
  And the level of a high frequency component is monitored, moving the optical system 1 at high speed toward the top P as mentioned above. Then, the optical system 1 is moved at high speed until the level of the high frequency component changes from the increasing tendency to the decreasing tendency and decreases by the predetermined level α, that is, to the point R shown in FIG. Make sure you did. Then, this time, the optical system 1 is moved from the R point in the opposite direction at a relatively slow speed, and the in-focus position P at which the level of the high-frequency component turns from increasing to decreasing is confirmed again. Later (that is, after reaching the point S in the figure), the optical system 1 is moved to the in-focus position P obtained by this confirmation at a relatively high speed, and a series of in-focus operations is completed.
[0044]
  In FIG. 1, moving the optical system 1 from the first O point to the Q point corresponds to the initial operation described in the claims, and is relatively fast from the Q point toward the R point. Moving at a speed corresponds to high-speed operation. Then, moving the optical system 1 from the R point to the S point at a relatively slow speed corresponds to the low-speed operation described in the claims, and a relatively fast speed from the S point to the in-focus position P. The movement by means of a fine adjustment operation.
[0045]
  Thus, also in the present embodiment, the in-focus position P is found by the hill-climbing method as in the conventional technique described above. However, according to the present embodiment, unlike the above-described conventional technique in which the optical system is moved at a low speed from the beginning, only the section from the R point to the S point in FIG. The optical system 1 is moved at a low speed. Therefore, it is possible to find the in-focus position P in a shorter time than in the conventional technique. In addition, the above-described moving the optical system 1 at a low speedRS sectionSince the in-focus position P is confirmed, the in-focus accuracy is maintained.
[0046]
  Further, as described above, when the illuminance of the subject decreases, the level of the high frequency component accordingly decreases as shown by a dotted line graph in FIG. 1, for example, and the change in the vicinity of the in-focus position P changes. Be gentle. Here, for example, if the relative difference α between the level of the high-frequency component at the in-focus position P and the level of the high-frequency component at the R point is constant, the lower the illuminance of the subject, the lower the difference between the in-focus position P and the R point. It is clear from FIG. 1 that the distance becomes longer and as a result, the focusing operation takes longer. Therefore, in the present embodiment, the relative difference α is changed in accordance with the illuminance of the subject detected by the illuminance detection circuit 4 described above. For example, when the illuminance of the subject is low as shown in FIG. By reducing the relative difference α, the distance between the in-focus position P and the R point is not increased. The relative difference α corresponds to the first level amount described in the claims.
[0047]
  Furthermore, as described above, depending on the performance and quality of the optical system 1, for example, as shown in FIG. 3, false resolutions P ′ and P ′ may occur at so-called out-of-focus positions other than the in-focus position P. Therefore, in the present embodiment, in order to prevent the false resolutions P ′ and P ′ from being mistakenly recognized as the in-focus position P, as shown in FIG. Is set in advance to a level β that is larger than the peak value and smaller than the level (maximum value) of the high-frequency component at the in-focus position P. Then, the maximum value of the level of the high-frequency component found by the series of focusing operations described above is compared with the level β, and when the maximum value is equal to or higher than the level β, the maximum value is set to the true alignment. Recognized as a focal position P.
[0048]
  On the other hand, when the maximum value is smaller than the level β, the maximum value is regarded as a peak of false resolutions P ′ and P ′. Then, the optical system 1 is moved at a low speed, for example, between the FAR side end and the NEAR side end over the entire moving range, and the position where the level of the high frequency component becomes maximum during this moving period is focused. Position P.
[0049]
  In general, it is known that the pseudo resolutions P ′ and P ′ also change according to the illuminance of the subject. Therefore, for example, if the level β is constant regardless of the illuminance of the subject, the peaks of the false resolutions P ′ and P ′ may be larger than the level β or the focus position depending on the illuminance of the subject. The level of the high frequency component in P may be smaller than the level β. In this case, it is possible to determine whether the maximum value of the level of the high-frequency component found by the series of focusing operations is the true focusing position P or the peaks of the false resolutions P ′ and P ′. become unable.
[0050]
  In order to eliminate such a problem, in the present embodiment, the level β is always set to false resolution P ′, P according to the illuminance of the subject detected by the illuminance detection circuit 4 described above. The level β is adjusted so as to be larger than the peak of “′” and smaller than the maximum value of the high-frequency component level in the entire moving region of the optical system 1. It should be noted that how much value the level β is set and how much the level β is changed according to the illuminance of the subject is obtained by experiments. And this level (beta) respond | corresponds to the 2nd level amount as described in a claim.
[0051]
  The series of focusing operations are controlled by the CPU in the control circuit 6 described above. The CPU controls the drive circuit 7 (generates a control signal) according to the flowchart shown in FIG. A series of focusing operations are realized. A program for operating the CPU according to the flowchart of FIG. 4 is stored in a ROM or RAM configuration storage unit (not shown) provided in the control circuit 6.
[0052]
  That is, the CPU (control circuit 6) first determines the above levels α and β according to the illuminance information of the subject obtained from the illuminance detector 4 (step S2). In step S2, the CPU determining the levels α and β corresponds to the first level variable means and the second level variable means described in the claims.
[0053]
  Then, the CPU moves the optical system 1 at a low speed by N pulses toward the FAR direction while monitoring the level of the high-frequency component obtained from the HPF 5 (step S4), and this movement increases the level of the high-frequency component. It is confirmed whether or not (step S6). The operations in steps S4 and S6 correspond to the initial operations described in the claims.
[0054]
  When the CPU confirms that the level of the high frequency component has increased in step S6 (YES in step S6), the CPU regards the optical system 1 as moving toward the in-focus position P, and continues as it is. This time, the optical system 1 is moved at a high speed in the same direction (step 8). On the other hand, when it is confirmed in step S6 that the level of the high frequency component has decreased (NO in step S6), the optical system 1 is regarded as moving in the direction opposite to the in-focus position P. The optical system 1 is moved at a high speed in the direction opposite to the above (step 10). The operations in steps S8 and S10 correspond to the high-speed operation described in the claims.
[0055]
  Then, in a state where the optical system 1 is moved at a high speed by the above step S8 or S10, the level of the high frequency component is decreasing from the increasing tendency until the optical system 1 reaches the FAR side end or the NEAR side end. Then, it is confirmed whether or not the peak value has decreased by the level α (steps S12 and S14). Here, when it is confirmed that the level of the high-frequency component has decreased by the level α from the peak value (YES in step S12), this time, in the direction opposite to the high-speed movement, The optical system 1 is moved at a low speed (step S16). The operation of moving the optical system 1 at a low speed in step S16 after exiting the loop composed of steps S12 and S14 corresponds to the low speed operation described in the claims.
[0056]
  Then, in a state where the optical system 1 is moved at a low speed in the step S16, the level of the high frequency component changes from an increasing tendency to a decreasing tendency until the optical system 1 reaches the FAR side end or the NEAR side end. Whether or not the peak value has been passed is confirmed (steps S18 and S20). Here, if it is confirmed that the level of the high-frequency component has passed the peak value (YES in step S18), it is then confirmed whether or not the peak value is greater than the level β described above ( Step 22).
[0057]
  If the peak value is larger than the level β in step S22 (YES in step S22), the CPU recognizes that the position corresponding to the peak value is the in-focus position P, and moves to that position. It moves at high speed (step S24), and a series of focusing operations are terminated. The operation of moving the optical system 1 to the in-focus position P at a high speed in this step S24 after exiting the loop consisting of the above steps S18 and S20 and step S22 is the fine adjustment described in the claims. Corresponds to the action.
[0058]
  On the other hand, when the peak value is smaller than the level β in step S22 (NO in step S22), the CPU determines that the position corresponding to the peak value is other than the in-focus position P, for example, false resolution P ′. , P ′ and proceed to step S26. In this step S26, the CPU moves the optical system 1 over its entire movement range, that is, between the FAR side end and the NEAR side end, for example, at a low speed, and the level of the high frequency component during this movement. Is found, and the process proceeds to step S24.
[0059]
  In steps S12 and S14, when the optical system 1 reaches the FAR side end or the NEAR side end before the level of the high frequency component decreases from the peak value by the level α (in step S14). In the case of YES), the CPU proceeds to step 26 described above. Further, in the above steps S18 and S20, when the optical system 1 reaches the FAR side end or the NEAR side end before the high-frequency component level changes from an increasing tendency to a decreasing tendency (in the case of YES in step S20). However, the CPU proceeds to step 26 described above.
[0060]
  By the way, in the above, the level β is set as shown in FIG. 3 in order not to mistake the peaks of the false resolutions P ′ and P ′ with the peak of the in-focus position P. Therefore, the influence of the false resolutions P ′ and P ′ can be avoided. This will be described with reference to FIG.
[0061]
  This is to confirm whether or not the level change amount Δ of the high frequency component in the OQ section in the initial operation is larger than a predetermined level difference γ, as shown in FIG. That is, the predetermined level difference γ is larger than the peak-to-peak value (A in the figure) of the false resolutions P ′ and P ′, and the peak-to-peak value in the entire high-frequency component (in the figure). A value smaller than B) is set. When the level change amount Δ of the high-frequency component in the OQ section is larger than the level difference γ, the subsequent movement direction of the optical system 1 is determined based on the increasing / decreasing tendency of the level change Δ. To do.
[0062]
  On the other hand, when the level change amount Δ of the high frequency component in the OQ section is less than the level difference γ, the optical system 1 is further moved in the same direction. Then, when the level change amount Δ of the high-frequency component due to this movement reaches the level γ, the subsequent movement direction of the optical system 1 is determined based on the increasing / decreasing tendency of the level change amount Δ. However, when the optical system 1 reaches the FAR side end or the NEAR side end before the level change amount Δ is less than the level γ, the optical system 1 is moved over the entire movement range, that is, A low-speed movement is made between the FAR-side end and the NEAR-side end, and the position where the level of the high-frequency component becomes maximum during this movement is set as the in-focus position P. Note that the level γ mentioned here corresponds to the third level difference described in the claims.
[0063]
  In order to realize the operation of FIG. 5, step S6 in the flowchart of FIG. 4 described above may be changed to a flowchart as shown in FIG.
[0064]
  That is, in step S4 in FIG. 4, after moving the optical system 1 by N pulses in the FAR direction, it is confirmed whether or not the level of the high frequency component has changed by the above level γ or more by this movement (step S4). S60). Here, when the level change of the high frequency component is equal to or higher than the level γ (in the case of YES), it is confirmed whether the level change tends to increase or decrease (step S62). In step S62, if it is determined that the level change tends to increase, the process proceeds to step S8 in FIG. 4, and if it is determined that the level change tends to decrease, the process proceeds to step S10.
[0065]
  On the other hand, if the level of the high-frequency component does not change more than the level γ in the step S60 (in the case of NO), the optical system 1 is further moved at a low speed in the same direction (step S64). Then, it is confirmed whether or not the level of the high frequency component has changed by the level γ before the optical system 1 reaches the FAR side end or the NEAR side end (steps S66 and S68). If it is confirmed that the level of the high frequency component has changed by the level difference γ or more (YES in step S66), the process proceeds to step S62. However, when the optical system 1 reaches the FAR side end or the NEAR side end without YES in the level difference γ or more (if YES in step S68), the step of FIG. Proceed to S10.
[0066]
  As for the level γ, the level γ always depends on the illuminance of the subject, that is, the illuminance information obtained from the illuminance detection circuit 4. -You may change so that it may become a value larger than the peak value A and smaller than the peak-to-peak value B in the whole high frequency component. In this case, step S in the flowchart of FIG.2In this case, programming may be performed so as to determine the levels of α, β, and γ according to the illuminance. In this step S2, the determination of the respective levels γ by the CPU corresponds to the third level variable means and the second level variable means described in the claims.
[0067]
  When the influence of the false resolutions P ′ and P ′ is avoided by comparing the level change amount Δ of the high-frequency component in the initial operation with the predetermined level γ, the above-described level β The procedure of comparing the level β and the peak value of the high-frequency component using is not an essential requirement. That is, when step S6 in the flowchart of FIG. 4 is replaced with the flowchart of FIG. 6, step S22 in the flowchart of FIG. 4 may be omitted. Of course, if step S22 is omitted, there is no need to determine the level β in step S2 in the flowchart of FIG.
[0068]
  In the present embodiment, when the focusing operation is started, the optical system 1 is first moved in the FAR direction. However, the optical system 1 may be moved in the opposite NEAR direction. Note that when this embodiment is applied to a camera that focuses on a relatively far side, such as a surveillance camera, for example, moving to the FAR side as described above may enable focusing in a shorter time. Is expensive.
[0069]
  In the present embodiment, the motor 8 that drives the optical system 1 is a stepping motor, but this is not a limitation. Further, the optical system 1 is not limited to a transmission system such as a lens, and a reflection system such as a reflection mirror may be used.
[0070]
【The invention's effect】
  As above1st inventionIn the autofocus device, as in the prior art described above, the in-focus position is found by the hill-climbing method. At this time, the optical system is moved at a low speed during low-speed operation (more specifically, the high-frequency component) The level is reduced from the level at the in-focus position by the first level amount until the in-focus position is confirmed). Therefore, there is an effect that the in-focus position can be found in a short time compared to the above-described conventional technique in which the optical system is moved at a low speed from the beginning. In addition, while realizing a reduction in the time of the focusing operation in this way, there is an effect that when the focusing position is confirmed, the optical system is in a low-speed operation state, so that high focusing accuracy can be ensured.
[0071]
  Furthermore, according to the first aspect of the invention, the second level is set in advance that is larger than the false resolution peak value and smaller than the high-frequency component level (maximum value) at the in-focus position. Then, the maximum value of the high frequency component level in the low speed operation is compared with the second level. Thus, it is determined whether the maximum value represents a true in-focus position or a false resolution peak. Therefore, unlike the above-described prior art, there is an effect that the false resolution is not erroneously recognized as the in-focus position.
[0072]
  In the second invention as well, as in the first invention, the in-focus position can be found in a short time. A third level difference that is larger than the peak-to-peak value of the false resolution and smaller than the peak-to-peak value in the entire high-frequency component is set in advance. The moving direction of the optical system in the high-speed operation is determined based on the increasing / decreasing tendency of the level change only when the level changes by more than the third level difference. Therefore, there is an effect that the moving direction of the optical system in the high-speed operation can be correctly determined without being affected by the false resolution.
[Brief description of the drawings]
FIG. 1 is a diagram conceptually showing a focusing operation of an autofocus device according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a schematic configuration of the embodiment.
FIG. 3 is a diagram conceptually illustrating a countermeasure when a false image is generated in a subject image in the embodiment.
FIG. 4 is a flowchart showing the operation of the control circuit in the same embodiment.
FIG. 5 is a diagram conceptually illustrating a coping method different from that in FIG. 3 when false resolution occurs in a subject image in the embodiment.
6 is a flowchart of a control circuit for realizing the operation of FIG.
FIG. 7 is a diagram conceptually showing a focusing operation in a conventional hill-climbing autofocus device.
FIG. 8 is a diagram illustrating a state in which false resolution occurs in a subject image in FIG.
[Explanation of symbols]
  1 Optical system
  2 Imaging device (imaging means)
  4 Illuminance detection circuit
  5 High pass filter (extraction means)
  6 Control circuit (control means, first level variable means, second level variable means, third level variable means)
  7 Drive circuit
  8 Motor (drive means)

Claims (6)

An optical system having an imaging function, an imaging means for converting a subject image formed by the optical system into a video signal, an extraction means for extracting a high frequency component from the video signal, and the extracted high frequency Control means for detecting a component level and generating a control signal based on the detected level, and moving the optical system along the optical axis direction based on the control signal to connect the optical system and the imaging means. Driving means for changing the distance to the image plane,
The control means includes
An initial operation of moving the optical system in a predetermined direction;
In this initial operation, when the level of the high-frequency component tends to increase, the optical system is moved at a high speed in the predetermined direction, and when the level of the high-frequency component tends to decrease, the optical system is referred to as the predetermined direction. High-speed movement to move in the opposite direction at high speed,
When the level of the high-frequency component changes from an increasing tendency to a decreasing tendency in this high-speed operation and decreases by a first level amount from the time of the change, the optical system is defined as the moving direction of the optical system in the high-speed operation. A low-speed operation that moves in the opposite direction at a speed slower than the moving speed in the high-speed operation,
After the level of the high frequency component was confirmed to have turned again decreasing from increasing in this low-speed operation, moves the optical system at a position recognized as the focus position of the optical system relative to the image plane Fine-tuning action,
Generating the control signal to cause the driving means to execute,
The control means compares the maximum value of the high-frequency component level in the low-speed operation with a second level, and the optical system corresponding to the maximum value when the maximum value is greater than or equal to the second level. Is detected as the in-focus position, and when the maximum value is smaller than the second level, the control signal is generated so as to move the optical system over the entire range in which the optical system can move. And recognizing the position where the level of the high-frequency component is maximum during the movement period of the optical system over the entire range as the in-focus position,
The second level is larger than the peak value of the false resolution when the false resolution occurs in the high frequency component, and is higher than the level of the high frequency component when the optical system is at the in-focus position. small,
Autofocus device.   2. The autofocus device according to claim 1, further comprising first level variable means for inputting the video signal and changing the first level amount in accordance with a signal level of the input video signal. 3. The autofocus device according to claim 1, further comprising a second level variable unit that receives the video signal and changes the second level according to a signal level of the input video signal . An optical system having an imaging function, an imaging means for converting a subject image formed by the optical system into a video signal, an extraction means for extracting a high frequency component from the video signal, and the extracted high frequency Control means for detecting a component level and generating a control signal based on the detected level, and moving the optical system along the optical axis direction based on the control signal to connect the optical system and the imaging means. Driving means for changing the distance to the image plane,
The control means includes
An initial operation of moving the optical system in a predetermined direction;
In this initial operation, when the level of the high-frequency component changes more than the third level difference and tends to increase, the optical system is moved at a high speed in the predetermined direction. In the initial operation, the level of the high-frequency component is the first level. When the optical system moves to one end of the movable range without changing more than three level differences or when the level of the high frequency component tends to decrease, the optical system is moved in a direction opposite to the predetermined direction. High-speed movement to move at high speed,
When this in high speed operation level of the high frequency component was reduced by a first amount of level from the time the rolling Ji was turned to decrease from increase, the optical system, the moving direction of the optical system in the high speed operation Is a low speed movement that moves in the opposite direction at a speed slower than the movement speed in the above high speed movement,
Fine adjustment to move the optical system to a position corresponding to the maximum value of the high-frequency component level in the low-speed operation after confirming that the high-frequency component level has changed again from an increasing tendency to a decreasing tendency in the low-speed operation. Operation and
Generating the control signal to cause the driving means to execute
The third level difference is larger than the peak-to-peak value of the false resolution when the false resolution occurs in the high-frequency component and smaller than the peak-to-peak value in the entire high-frequency component. ,
Autofocus device. 5. The autofocus device according to claim 4 , further comprising first level variable means for inputting the video signal and changing the first level amount in accordance with a signal level of the input video signal . 6. The autofocus device according to claim 4, further comprising third level variable means for inputting the video signal and changing the third level difference in accordance with a signal level of the input video signal.

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